Preheat the Oven: Preheat your oven to 350°F (175°C) and line a cupcake pan with paper liners.
Mix Dry Ingredients: In a large bowl, combine flour, sugar, cocoa powder, baking soda, baking powder, and salt. Whisk until well mixed.
Combine Wet Ingredients: In a separate bowl, whisk together the melted butter, eggs, milk, and vanilla extract until smooth.
Combine Mixtures: Gradually add the wet ingredients into the dry ingredients, stirring until just combined; be careful not to over-mix.
Fill Cupcake Liners: Pour or spoon the batter into the cupcake liners, filling each about 2/3 full.
Bake: Place in the oven and bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Cool Completely: Remove from the oven and let the cupcakes cool in the pan for a few minutes before transferring them to a wire rack to cool completely.
Make Strawberry Buttercream: While the cupcakes are cooling, beat the softened butter in a mixing bowl until creamy. Gradually add powdered sugar and strawberry puree, mixing until well combined. If needed, add a bit of milk for the desired consistency.
Frost the Cupcakes: Once the cupcakes are completely cool, frost them generously with the strawberry buttercream using a piping bag or a spatula.